1. Technical Field
The present invention relates to a liquid-ejecting head which changes the pressure in a pressure-generating chamber communicating with a nozzle opening and which includes a piezoelectric layer and electrodes for applying a voltage to the piezoelectric layer and also relates to a liquid-ejecting apparatus.
2. Related Art
Piezoelectric elements each include two electrodes and a piezoelectric layer which is made of a piezoelectric material, such as a crystallized piezoelectric material, having an electromechanical transducing function and which is sandwiched between the electrodes. The piezoelectric elements are used as, for example, flexural vibration-mode actuators and are mounted in liquid-ejecting apparatuses. Typical example of the liquid-ejecting apparatuses are ink jet recording heads which include diagrams forming portions of pressure-generating chambers communicating with nozzle openings for ejecting ink droplets and which eject ink droplets in such a manner that the diagrams are deformed with piezoelectric elements such that ink in the pressure-generating chambers is pressurized.
A piezoelectric material for use in piezoelectric layers (piezoelectric ceramics) making up the piezoelectric elements need to have high piezoelectric properties. A typical example of the piezoelectric material is lead zirconate titanate (PZT) (see JP-A-2001-223404). The piezoelectric layers are formed in such a manner that, for example, a colloid solution prepared by dissolving an organometallic compound in a solvent is applied to a target, is heated, and is then crystallized into the piezoelectric layers, which are filmy. Known examples of processes for forming the piezoelectric layers include chemical solution processes such as sol-gel processes and metal-organic deposition (MOD) processes.
A ferroelectric such as lead zirconate titanate has domains having polarization axes in random directions when being in an unpolarized state. Therefore, an unpolarized piezoelectric layer made of the ferroelectric does not expand or contract. In order to use the ferroelectric as a piezoelectric, the ferroelectric needs to be polarized in such a manner that an electric field is applied to the ferroelectric in a single direction such that the polarization axes are aligned with each other. For the above filmy piezoelectric layers, a voltage not greater than a voltage Vc, referred to as a midpoint potential, sufficient to create a coercive electric field Ec is continuously applied to each filmy piezoelectric layer such that polarization axes are aligned in a predetermined direction, a diagram is deformed by applying a pulse to the diagram on the basis of the midpoint potential, and the pressure in a pressure chamber is thereby changed, whereby ink is ejected. In order to drive a piezoelectric element including a filmy piezoelectric layer made of lead zirconate titanate, a midpoint potential not less than the coercive electric field Ec needs to be applied to the piezoelectric element. Therefore, the piezoelectric element has a problem that the piezoelectric element is unlikely to be driven at low voltage. In awareness of environment issues, piezoelectric materials with a reduced lead content are being demanded.